Polishing composition for magnetic disk

ABSTRACT

A polishing composition for a magnetic disk, comprising alumina, water, a peroxide and an organic acid; a polishing process for a substrate to be polished, comprising the step of polishing the substrate to be polished with the polishing composition; and a process for manufacturing a substrate, comprising the step of polishing a substrate to be polished with the polishing composition. The polishing composition can be suitably used for the manufacture of a magnetic disk substrate for high-quality hard disks and the like.

FIELD OF THE INVENTION

The present invention relates to a polishing composition for a magneticdisk, a polishing process with the polishing composition, and a methodfor manufacturing a substrate with the polishing composition.

BACKGROUND OF THE INVENTION

In order to have a smaller unit recording area and promote higherstorage capacity for hard disk drives, it has been desired to lower theflying height of the magnetic head and prevent surface defects (surfacestains). In order to lower the flying height of the magnetic head, therehave been earnestly desired a reduction of short-wavelength waviness(waviness having a wavelength of 50 to 500 μm) and a reduction oflong-wavelength waviness (waviness having a wavelength of 0.5 mm ormore), and prevention of residual substances on the surface during thepolishing step of the hard disk substrate. The “waviness” as used hereinrefers to dents and projections of a surface having a wavelength longerthan that of roughness, and can be determined by using opticalinstruments represented by “Zygo” commercially available from CanonSales Inc. In order to manufacture a substrate with reduced waviness andsurface stains as described above, mechanical conditions such as thepore size control of a polishing pad, hardness control, polishing loadduring polishing and control of the number of rotations have beenstudied. However, although the mechanical conditions as mentioned abovehave some effects, they cannot be said to be satisfactory. On the otherhand, an approach from a polishing composition has been studied.Japanese Patent Laid-Open No. 2003-14733 discloses a polishingcomposition containing an oxidizing agent, a phosphorus-containinginorganic acid, and other organic acid. Japanese Patent Laid-Open No.Hei 11-246849 discloses a slurry for a polishing step, containingabrasive particles, hydrogen peroxide, a metal nitrate and nitric acid.However, the approaches from these polishing compositions cannot besatisfactory from the viewpoint of satisfying both the polishing rateand reduction in waviness necessary for practical use, and also theprevention of surface stains.

SUMMARY OF THE INVENTION

The present invention relates to the followings:

-   -   [1] a polishing composition for a magnetic disk, containing        alumina, water, a peroxide and an organic acid;    -   [2] a polishing process of a substrate to be polished, including        the step of polishing the substrate to be polished with the        polishing composition of the above [1]; and    -   [3] a method for manufacturing a substrate, including the step        of polishing a substrate to be polished with the polishing        composition of the above [1].

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a polishing composition capable ofhaving a high polishing rate and reduced waviness. Also, the presentinvention relates to a polishing process for, for instance, reducingwaviness of a substrate to be polished with the polishing composition;and a method for manufacturing a substrate with the polishingcomposition.

These and other advantages of the present invention will be apparentfrom the following description.

By using the polishing composition of the present invention for thepolishing of a magnetic disk, there are exhibited some effects that ahigh polishing rate and reduction in waviness of an object to bepolished can be accomplished, and defects in a substrate, especiallystains on a substrate can be reduced. Also, there are provided apolishing process for reducing waviness of a substrate to be polishedwith the polishing composition, and a method for manufacturing asubstrate with the polishing composition.

One of the significant features of the polishing composition of thepresent invention resides in the combined use of an organic acid and aperoxide as polishing accelerators of the polishing composition, whereinan alumina is used as an abrasive. By using the polishing compositionhaving the above features, a remarkable effect is exhibited such asachievement of a high polishing rate, reduction in waviness of asubstrate to be polished, and sufficient reduction in surface defectssuch as scratches and pits, especially surface stains.

The details of the functional mechanism for polishing with the polishingcomposition of the present invention may not be certain. Although notwanting to be limited by theory, it is presumed that the lower the pH ofthe polishing composition during polishing, the higher the polishingrate, so that an etching effect on an object to be polished is caused bythe hydrogen ion generated by the acid, whereby the polishing isaccelerated. Accordingly, the higher the acid strength, the higher thepolishing rate. In addition, the peroxide changes the surface of theobject to be polished so that the polishing effect of the alumina issatisfactorily exhibited, thereby increasing the above-mentioned etchingeffect. Consequently, the waviness can be reduced at the processingspeed on the actual manufacturing level. Although not wanting to belimited by theory, it is presumed that the amplifying effect by thecombination of the organic acid and the peroxide is simultaneouslyconnected to the reduction of the substrate defect, especially thereduction of substrate stains.

The polishing composition of the present invention contains an aluminaas an abrasive. As the alumina preferable in the present invention, thealumina has a purity as alumina of preferably 95% or more, morepreferably 97% or more, and even more preferably 99% of more, from theviewpoints of reducing the waviness, reducing the surface roughness,increasing the polishing rate and preventing the surface defects. Theα-alumina is preferable, from the viewpoint of the polishing rate, andthe intermediate alumina such as γ-alumina, δ-alumina, θ-alumina,η-alumina, and κ-alumina are preferable, from the viewpoints of thesurface conditions and reduction in the waviness. The intermediatealumina in the present invention is a generic term referring to aluminaparticles other than the α-alumina particles, and concrete examplesthereof include γ-alumina particles, δ-alumina particles, θ-aluminaparticles, η-alumina particles, κ-alumina particles, and mixturesthereof. Among these intermediate aluminas, γ-alumina, δ-alumina,θ-alumina, and mixtures thereof are preferable, from the viewpoints ofincreasing the polishing rate and reducing the waviness, and γ-aluminaand θ-alumina are more preferable.

The alumina has an average primary particle size of preferably from0.005 to 0.8 μm, more preferably from 0.01 to 0.4 μm, from the viewpointof reducing the waviness, and an average secondary particle size ofpreferably from 0.01 to 2 μm, more preferably from 0.05 to 1.0 μm, andeven more preferably from 0.1 to 0.5 μm. The average primary particlesize of the abrasive may be obtained by subjecting the abrasive to animage analysis by observing with a scanning electron microscope(preferably from 3000 to 30000 times) or a transmission electronmicroscope (preferably from 10000 to 300000 times), and determining theparticle size. In addition, the average secondary particle size may bedetermined as a volume-average particle size by using a laserdiffraction method.

Especially, when the alumina is an intermediate alumina, the specificsurface area determined by the BET method is preferably from 30 to 300m²/g, more preferably from 50 to 200 m²/g.

The content of the alumina is preferably 0.05% by weight or more, morepreferably 0.1% by weight or more, even more preferably 0.5% by weightor more, and even more preferably 1% by weight or more, of the polishingcomposition, from the viewpoints of increasing the polishing rate andreducing the waviness. Also, the content is preferably 40% by weight orless, more preferably 30% by weight or less, even more preferably 25% byweight or less, and even more preferably 20% by weight or less, of thepolishing composition, from the viewpoints of the surface quality andeconomic advantages. Specifically, the content of the alumina ispreferably from 0.05 to 40% by weight, more preferably from 0.1 to 30%by weight, even more preferably from 0.5 to 25% by weight, and even morepreferably from 1 to 20% by weight, of the polishing composition.

The polishing composition of the present invention contains a peroxide,from the viewpoints of benefits such as increasing the polishing rateand reducing the waviness. The peroxide of the present invention isroughly classified into inorganic peroxides and organic peroxidesaccording to their structures. Concrete examples of the peroxides are asfollows. As the inorganic peroxides, hydrogen peroxide, peroxides ofalkali metals or the alkaline earth metals, such as sodium peroxide,potassium peroxide, calcium peroxide, barium peroxide and magnesiumperoxide; peroxocarbonates, such as sodium peroxocarbonate and potassiumperoxocarbonate; peroxosulfuric acids or salts thereof, such as ammoniumperoxodisulfate, sodium peroxodisulfate, potassium peroxodisulfate andperoxomonosulfuric acid; peroxonitric acids and salts thereof, such asperoxonitric acid, sodium peroxonitrate and potassium peroxonitrate;peroxophosphoric acids or salts thereof, such as sodium peroxophosphate,potassium peroxophosphate and ammonium peroxophosphate; peroxoboricacids and salts thereof, such as sodium peroxoborate and potassiumperoxoborate; peroxochromic acids and salts thereof, such as potassiumperoxochromate and sodium peroxochromate; permanganates, such aspotassium permanganate and sodium permanganate; halogen-containingoxyacids and derivatives thereof, such as sodium perchlorate, potassiumperchlorate, chloric acid, sodium hypochlorite, sodium periodate,potassium periodate, iodic acid and sodium iodate may be used. As theorganic peroxides, percarboxylic acids, such as peracetic acid,performic acid and perbenzoic acid; peroxides, such as t-butyl peroxideand cumene peroxide may be used. Among them, the inorganic peroxide ispreferable, because of increase in the polishing rate and easy handlingsuch as availability and water-solubility. Moreover, in consideration ofthe environmental problems, an inorganic peroxide which does not containa heavy metal is preferable. From the above viewpoint, the inorganicperoxide is more preferable, and hydrogen peroxide, peroxosulfates,halogen-containing oxyacids and salts thereof are even more preferable,and hydrogen peroxide is even more preferable. These peroxides can beused alone or in admixture of two or more kinds.

The content of the peroxide is preferably 0.002% by weight or more, morepreferably 0.005% by weight or more, even more preferably 0.007% byweight or more, and even more preferably 0.01% by weight or more, of thepolishing composition, from the viewpoints of increasing the polishingrate and reducing the waviness. The content is preferably 20% by weightor less, more preferably 15% by weight or less, even more preferably 10%by weight or less, and even more preferably 5% by weight or less, of thepolishing composition, from the viewpoints of the surface quality andeconomic advantages. Specifically, the content of the peroxide ispreferably from 0.002 to 20% by weight, more preferably from 0.005 to15% by weight, even more preferably 0.007 to 10% by weight, and evenmore preferably from 0.01 to 5% by weight, of the polishing composition.

The polishing composition of the present invention contains an organicacid in addition to the alumina and the peroxide, from the viewpoints ofbenefits such as increasing the polishing rate and reducing thewaviness. The organic acid usable in the present invention has a pK1 ofpreferably 7 or less, more preferably 5 or less, even more preferably 4or less, and even more preferably 2 or less, from the viewpoints ofincreasing the polishing rate and reducing the waviness. Here, the pK1is expressed as a logarithmic value of an inverse of a first aciddissociation constant at 25° C. The pK1 of each compound is listed inKagaku Binran (Kiso-hen) II, Fourth Revision, pp. 316-325 (Edit. byNippon Kagakukai), and the like.

As the organic acid preferable in the present invention,sulfur-containing organic acids, carboxylic acids andphosphor-containing organic acids are preferable, from the viewpoints ofincreasing the polishing rate, reducing the waviness and preventing thesurface stains. Concrete examples thereof are as follows: Monocarboxylicacids, such as formic acid, acetic acid, glycolic acid, lactic acid,propanoic acid, hydroxypropanoic acid, butyric acid, benzoic acid, andglycine; polycarboxylic acids, such as oxalic acid, succinic acid,glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid,malic acid, tartaric acid, citric acid, isocitric acid, phthalic acid,nitrilotriacetic acid and ethylenediaminetetraacetic acid;sulfur-containing organic acids, such as methanesulfonic acid andparatoluenesulfonic acid; phosphor-containing organic acids, such asethylphosphoric acid, butylphosphoric acid, laurylphosphoric acid,phosphonohydroxyacetic acid, hydroxyethylidene-1,1-diphosphonic acid,phosphonobutane tricarboxylic acid and ethylenediaminetetramethylenephosphonic acid; and the like. Among them, the sulfur-containing organicacids or the phosphor-containing organic acids are preferable, morepreferably organic sulfonic acids or organophosphonic acids, and evenmore preferably organic sulfonic acids, from the viewpoints ofincreasing the polishing rate and reducing the waviness. Additionally,the sulfur-containing organic acids and carboxylic acids are preferable,more preferably organic sulfonic acids and polycarboxylic acids, fromthe viewpoints of preventing the surface stains of the object to bepolished.

These compounds can be used alone or in admixture.

The content of the organic acid is preferably 0.002% by weight or more,more preferably 0.005% by weight or more, even more preferably 0.007% byweight or more, and even more preferably 0.01% by weight or more, of thepolishing composition, from the viewpoints of increasing the polishingrate and reducing the waviness. Also, the content is preferably 20% byweight or less, more preferably 15% by weight or less, even morepreferably 10% by weight or less, and even more preferably 5% by weightor less, of the polishing composition, from the viewpoints of thesurface quality and economic advantages. Specifically, the content ofthe acid is preferably from 0.002 to 20% by weight, more preferably from0.005 to 15% by weight, even more preferably from 0.007 to 10% byweight, and even more preferably from 0.01 to 5% by weight, of thepolishing composition.

Water in the polishing composition of the present invention is used as amedium. The content of water is preferably from 55 to 99% by weight,more preferably from 60 to 97% by weight, and even more preferably from70 to 95% by weight, from the viewpoint of efficiently polishing theobject to be polished.

It is preferable that an inorganic acid is used together in thepolishing composition of the present invention, from the viewpoints offurther increasing the polishing rate and reducing the waviness. Theinorganic acid includes nitrogen-containing inorganic acids, such asnitric acid and nitrous acid; sulfur-containing inorganic acids, such assulfuric acid, sulfurous acid and amide sulfuric acid;phosphor-containing inorganic acids, such as phosphoric acid,pyrophosphoric acid, polyphosphoric acid and phosphonic acid, and thelike. Among them, nitric acid, nitrous acid, sulfuric acid, sulfurousacid and amide sulfuric acid are preferable, more preferably sulfuricacid, sulfurous acid and amide sulfuric acid, and even more preferablysulfuric acid, from the viewpoint of increasing the polishing rate. Whenthe inorganic acid is used together, the content of the inorganic acidis preferably 0.002% by weight or more, more preferably 0.005% by weightor more, even more preferably 0.007% by weight or more, and even morepreferably 0.01% by weight or more, of the polishing composition. Thecontent is preferably 20% by weight or less, more preferably 15% byweight or less, even more preferably 10% by weight or less, and evenmore preferably 5% by weight or less, of the polishing composition, fromthe viewpoints of the surface quality and economic advantages.Specifically, the content of the inorganic acid is preferably from 0.002to 20% by weight, more preferably from 0.005 to 15% by weight, even morepreferably from 0.007 to 10% by weight, and even more preferably from0.01 to 5% by weight, of the polishing composition.

In addition, there can be added one or more components such as aninorganic salt, a thickener, an anticorrosive agent or a basic substanceto the polishing composition of the present invention, as occasiondemands. Especially, the inorganic salt such as ammonium nitrate,ammonium sulfate, potassium sulfate, nickel sulfate, aluminum sulfate orammonium sulfaminate has a subsidiary effect for increasing thepolishing rate. These other components can be used alone or in admixtureof two or more kinds. Also, the content of the other components ispreferably from 0.05 to 20% by weight, more preferably from 0.05 to 10%by weight, and even more preferably from 0.05 to 5% by weight, of thepolishing composition, from the viewpoint of economic advantages.

There can be further added one or more components, such as adisinfectant or an antibacterial agent, as occasion demands. The contentof the disinfectant or the antibacterial agent is preferably from 0.0001to 0.1% by weight, more preferably from 0.001 to 0.05% by weight, andeven more preferably from 0.002 to 0.02% by weight, of the polishingcomposition, from the viewpoint of exhibiting its function and from theviewpoints of the influence on polishing performance and economicadvantages.

The concentration of each component of the polishing composition of thepresent invention is a concentration at which polishing is preferablycarried out, and may be the concentration during the preparation of thecomposition. In many cases, the composition is usually prepared as aconcentrate, which is diluted before use or upon use.

The polishing composition can be prepared by adding or mixing theintended components by an optional method.

It is preferable that the pH of the polishing composition isappropriately determined depending upon the kinds of the object to bepolished and the required properties. The lower the pH, the morepreferable, from the viewpoints of increasing the polishing rate andreducing the waviness, and the closer the pH of 7, the more preferable,from the viewpoints of prevention of the corrosion of the processingmachine and safety for an operator. Accordingly, considering bothviewpoints, the pH is preferably 0.1 or more and less than 6, morepreferably 0.5 or more and less than 5, even more preferably 1 or moreand less than 4, and even more preferably 1 or more and less than 3. ThepH of the polishing composition can be adjusted by properly adding aninorganic acid, such as nitric acid or sulfuric acid; an organic acid,such as a hydroxycarboxylic acid or a polycarboxylic acid, anaminopolycarboxylic acid, an amino acid, a metal salt or an ammoniumsalt thereof; or a basic substance, such as, an aqueous ammonia, sodiumhydroxide, potassium hydroxide or an amine, in a desired amount.

The method for manufacturing a substrate of the present inventionincludes the step of polishing a substrate to be polished with theabove-mentioned polishing composition.

The magnetic disk substrate which is the substrate to be polished as asubject for the present invention is used as the substrate for magneticrecording media. Concrete examples of the magnetic disk substratesinclude representatively a substrate made of an aluminum alloy platedwith Ni—P, and there are also included a substrate made of glass orglassy carbon, instead of aluminum alloy, and plated with Ni—P thereon;or a substrate coated with various metallic compounds by plating ordeposition, instead of the substrate plated with Ni—P.

In the above-mentioned polishing process, the object to be polished maybe polished by clamping a substrate with polishing platens to which apolishing cloth made of a porous organic polymer and the like is pasted;feeding the polishing composition of the present invention to a surfaceto be polished of the substrate; and moving the polishing platens or thesubstrate, while applying pressure. Accordingly, the present inventionrelates to a polishing process for a substrate to be polished, includingthe step of polishing the substrate with the above-mentioned polishingcomposition. Other conditions such as the kind of polishing machine,polishing temperature, polishing rate and feed amount of the polishingcomposition are not particularly limited.

The polishing composition of the present invention is especiallyeffective in the polishing step, and the polishing composition can besimilarly applied to other steps than this, for instance, the lappingstep, and the like.

EXAMPLES

The following examples further describe and demonstrate embodiments ofthe present invention. The examples are given solely for the purposes ofillustration and are not to be construed as limitations of the presentinvention.

Examples 1 to 6, Comparative Examples 1 and 2

1. Preparation of Polishing Composition

Given amounts of alumina (average secondary particle size: 0.2 μm,purity: about 99.9%), a peroxide, an organic acid, other additives asshown in Table 1, and balance ion-exchanged water were formulated whilestirring, to give a polishing composition.

2. Polishing Process

Each of the polishing compositions obtained in the Examples andComparative Examples was evaluated for its polishing properties bypolishing a Ni—P plated, aluminum alloy substrate having a thickness of1.27 mm, and a diameter of 3.5 inch (95 mm) (short-wavelength waviness:3.8 nm and long-wavelength waviness: 1.6 nm, as determined by ZygoNew-View 200), using a double-sided processing machine under thefollowing setting conditions, to give an object to be polished made ofNi—P plated aluminum alloy substrate usable as a substrate for amagnetic recording medium.

The setting conditions for the double-sided processing machine are asfollows.

<Setting Conditions for Double-Sided Processing Machine]

Double-sided processing machine: Model 9B, commercially available fromSPEEDFAM CO., LTD.

-   -   Processing pressure: 9.8 kPa    -   Polishing pad: “H9900” (trade name, commercially available from        FUJIBO)    -   Rotational speed of a lower platen: 50 r/min.    -   Feeding amount for a polishing composition: 100 ml/min    -   Polishing time period: 4 min.    -   Number of substrates introduced: 10        3. Evaluation Methods        (1) Polishing Rate

Weights of each substrate before and after polishing were measured usinga device commercially available from Sartorius under the trade name ofBP-210S. Change in weight of each substrate was obtained, and an averageof 10 substrates was referred to as an amount reduced; and a valueobtained by dividing the amount reduced by the polishing time isreferred to as a rate of weight reduced. The rate of weight reduced isintroduced into the following equation and converted to a polishing rate(μm/min). A relative value of a polishing rate (relative rate) for eachof the Examples and Comparative Examples was obtained, assuming that thepolishing rate of Comparative Example 1 takes a standard value of 1.Rate of Weight Reduced (g/min)=[Weight Before Polishing (g)−Weight AfterPolishing (g)]/Polishing Time (min)Polishing Rate (μm/min)=Rate of Weight Reduced (g/min)/Area of One Sideof Substrate (mm²)/Ni—P Plating Density (g/cm³)×1000000(2) Waviness

The waviness of each substrate after the polishing was determined forshort-wavelength waviness and long-wavelength waviness at two points of180° intervals (total of 4 points) under the conditions mentioned below.Device: Zygo New-View 200 commercially available from Canon Sales, Inc.Object Lens: Magnification, 2.5 times, Michelson Zooming Ratio: 0.5Remove: Cylinder Filter type: FFT Fixed Band Pass Short-WavelengthWaviness: Filter High Wavelength 50 μm Filter Low Wavelength 500 μmLong-Wavelength Waviness: Filter High Wavelength 0.5 mm Filter LowWavelength 5 mm Area: 4.33 mm × 5.77 mm(3) Surface Stains

The surface of each substrate after the polishing was observed with apolarization optical microscope at a magnification of 300-folds, and thefollowing 5-rank evaluations were made. Here, those ranked in 1 and 2are failures from the viewpoint of practical purposes.

-   -   5: no alumina residue and polishing debris are observed on the        surface at all;    -   4: alumina residue and polishing debris are observed but in very        little amounts;    -   3: alumina residue and polishing debris are observed but in        slight amounts;    -   2: alumina residue and polishing debris are observed but in        large amounts; and    -   1: alumina residue and polishing debris are observed but in very        large amounts.

The results are shown in Table 1. TABLE 1 Waviness Polishing Short-Long- Composition of Polishing Composition (% by weight) RateWavelength, Wavelength, % by % by Organic % by Other % by RelativeRelative Relative Surface Alumina wt. Peroxide wt. Acid wt. Additive wt.pH Value Value Value Stains Ex. No. Ex. 1 α-Alumina 4 Hydrogen 0.5Citric Acid 3.3 — — 2.0 1.2 0.95 0.74 5 Peroxide Ex. 2 α-Alumina 4Hydrogen 0.5 Citric Acid 3.3 Sulfuric 0.4 1.2 1.6 0.90 0.69 5 PeroxideAcid Ex. 3 α-Alumina 4 Hydrogen 0.5 Citric Acid 1.2 Sulfuric 0.2 1.4 1.50.88 0.65 5 Peroxide Acid Ammonium 2.0 Sulfate Ex. 4 α-Alumina 4Hydrogen 0.5 Tartaric Acid 3.3 — — 2.0 1.1 0.97 0.76 4 Peroxide Ex. 5α-Alumina 4 Hydrogen 0.5 Methane- 1.5 — — 0.7 1.5 0.93 0.71 3 Peroxidesulfonic Acid Ex. 6 α-Alumina 4 Hydrogen 0.5 Hydroxy- 1.6 — — 1.4 1.20.89 0.68 3 Peroxide ethylidene Diphos- phonic Acid Comp. Ex. No. Comp.α-Alumina 4 Hydrogen 0.5 — — Phosphoric 1.5 1.2 1.0 1.00 1.00 1 Ex. 1Peroxide Acid Nitric Acid 0.5 Comp. α-Alumina 4 Hydrogen 0.5 — — NitricAcid 0.1 2.2 0.9 1.05 1.07 1 Ex. 2 Peroxide Aluminum 1.2 Nitrate

Waviness Short- Long- Wavelength, Wavelength, Polishing Rate RelativeRelative Surface Relative Value Value Value Stains Ex. No. Ex. 1 1.20.95 0.74 5 Ex .2 1.6 0.90 0.69 5 Ex. 3 1.5 0.88 0.65 5 Ex. 4 1.1 0.970.76 4 Ex. 5 1.5 0.93 0.71 3 Ex. 6 1.2 0.89 0.68 3 Comp. Ex. No. Comp.1.0 1.00 1.00 1 Ex. 1 Comp. 0.9 1.05 1.07 1 Ex. 2

It can be seen from the results of Table 1 that the polishingcompositions obtained in Examples 1 to 6 have high polishing rates, arecapable of reducing both the short-wavelength waviness and thelong-wavelength waviness, and further capable of remarkably reducingsurface stains of a substrate.

The polishing composition of the present invention can be suitably usedfor the manufacture of a magnetic disk substrate for high-quality harddisks and the like.

The present invention being thus described, it will be obvious that thesame may be varied in many ways. Such variations are not to be regardedas a departure from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A polishing composition for a magnetic disk, comprising alumina,water, a peroxide and an organic acid.
 2. The polishing compositionaccording to claim 1, wherein the organic acid is one or more membersselected from the group consisting of sulfur-containing organic acids,carboxylic acids, and phosphorus-containing organic acids.
 3. Thepolishing composition according to claim 1 or 2, further comprising aninorganic acid.
 4. The polishing composition according to claim 1,wherein the composition has a pH of 0.1 or more and less than
 6. 5. Thepolishing composition according to claim 3, wherein the composition hasa pH of 0.1 or more and less than
 6. 6. A polishing process for asubstrate to be polished, comprising the step of polishing the substrateto be polished with the polishing composition of claim
 1. 7. A polishingprocess for a substrate to be polished, comprising the step of polishingthe substrate to be polished with the polishing composition of claim 3.8. The polishing process according to claim 6, wherein the substrate tobe polished is a substrate produced by plating an aluminum alloy with aNi—P alloy.
 9. The polishing process according to claim 7, wherein thesubstrate to be polished is a substrate produced by plating an aluminumalloy with a Ni—P alloy.
 10. A process for manufacturing a substrate,comprising the step of polishing a substrate to be polished with thepolishing composition of claim
 1. 11. A process for manufacturing asubstrate, comprising the step of polishing a substrate to be polishedwith the polishing composition of claim
 3. 12. The process according toclaim 10, wherein the substrate to be polished is a substrate producedby plating an aluminum alloy with a Ni—P alloy.
 13. The processaccording to claim 11, wherein the substrate to be polished is asubstrate produced by plating an aluminum alloy with a Ni—P alloy.